Getting Into The Stardew Valley Sewer
The Sewer is a hard to reach area in Stardew Valley. It hosts a variety of rare items and some key items you will need to complete the Witch’s Swamp questlines. The Sewer can only be opened once you have acquired the Rusty Key and has two entrances in the valley. It is made up of only two areas but has some huge benefits waiting for you in both of them including being able to get the rare merchandise that you can’t find in any other part of the game.
Entering The Sewer
To enter the Sewer, you will need to get the key from the museum. To do this, it’s going to take you quite a bit of time. You have to be able to donate exactly 60 items to the musuem to get the key as a reward. After you donate the 60 items, the next morning, Gunther will show up at your house and hand you the item. From there, either go to the entrance in Cindersap Forest or in the town near the bottom of the area. Once you enter, you will be able to complete the quest Dark Talisman and open another area in the valley.
When you enter the sewer, you will notice that it has an inhabitant named Krobus. Krobus is the only friendly monster in the game and a rare goods merchant to boot. He will be able to tell you where the Dark Talisman is located and sell you the Return Scepter, an item that can warp you back home from anywhere on the map. He is also an easy source of Iridium Sprinklers and sells one each Friday for 10,000G each. You will also need him to get one of the Stardrops in the game.
Bugs and Fish In The Stardew Valley Sewer
The second area of the sewer will have you wading through what looks to be a bug infested swamp. The area will be blocked off until the endgame quest, the Dark Talisman. In order to trigger this area you will need to either finish buying the renovations from Joja or finish all the bundles in the Community Center. The Mutant Bug Lair is full of mutant larva that can turn into mutant bugs and chase you down across the area. It is the room featuring the most enemies in the game and your reward for completing it is a treasure chest with the Dark Talisman inside.
You will also need to unlock the sewer to finish your fishing log. The sewer houses one of the legendary fish, the Mutant Carp. The carp is one of only two fish you catch in the sewer and is available to be caught year round, unlike the other legendary fish. The Mutant Carp sells for over 1,000G, but is difficult to fish up due to the high catch rate of trash from the Sewer waters. The Mutant Bug Lair connected to the sewer also contains the only way to get a Slimejack. The Slimejack can only be caught to 2pm.